scholarly journals Resistive Processes in the Preflare Phase of Eruptive Flares

1998 ◽  
Vol 188 ◽  
pp. 207-208
Author(s):  
T. Magara ◽  
K. Shibata
Keyword(s):  
Current Sheet ◽  
Current Density ◽  
Solar Flares ◽  
Magnetic Pressure ◽  
Anomalous Resistivity ◽  
Magnetic Island ◽  
Tearing Instability ◽  
Mhd Simulations ◽  
A Current

In this study, we perform 2.5-dimensional MHD simulations and clarify the role of perpendicular magnetic fields (which are perpendicular to the 2D plane) in a preflare current sheet of solar flares. At the first stage, a current sheet formed within a coronal magnetic structure is filled with the perpendicular fields (force-free structure). Then this sheet begins to be dissipated through the tearing instability under a uniform resistivity. As the instability proceeds, the distribution of the perpendicular fields vary in such a way that most of them gather around O-point (magnetic island) instead of X-point. Therefore, the magnetic pressure of these fields weaken in the vicinity of X-point so that they no longer suppress the inflows toward this point. These flows then make the current sheet thinner and thinner, which implies that the current density around X-point becomes high enough to cause an anomalous resistivity whose value is much larger than that of the normal collisional resistivity. In this way, the transition from a uniform resistivity to a locally-enhanced one occurs, which can make the violent energy release observed in solar flares.

Forced reconnexion by fast magnetosonic waves in a current sheet with stagnation-point flows

1983 ◽  
Vol 30 (1) ◽  
pp. 109-124 ◽  
Author(s):  
Jun-Ichi Sakai
Keyword(s):  
Current Sheet ◽  
Stagnation Point ◽  
Solar Flares ◽  
Ponderomotive Force ◽  
Magnetosonic Wave ◽  
Fast Wave ◽  
Tearing Mode ◽  
Tearing Modes ◽  
Tearing Instability ◽  
A Current

Forced reconnexion due to tearing modes driven by fast magnetosonic waves in a current sheet with stagnation-point flows is discussed. The current sheet with stagnation-point flows which is weakly unstable against tearing modes can be strongly destabilized by vortex motions due to the ponderomotive force of the fast magnetosonic wave. This forced tearing instability can be driven when the incident fast magnetosonic wave intensity, I, exceeds a critical value given by where is the Alfvén velocity, vg the group velocity of the fast wave, vo the background inflow velocity, l the thickness of the current sheet and k the wavenumber of the forced tearing mode. The growth rate is estimated. Applications to solar flares and magnetopause reconnexion processes are briefly discussed.

scholarly journals Flare particle acceleration in the interaction of twisted coronal flux ropes

2018 ◽  
Vol 611 ◽  
pp. A40 ◽  
Author(s):  
J. Threlfall ◽  
A. W. Hood ◽  
P. K. Browning
Keyword(s):  
Particle Acceleration ◽  
Solar Flares ◽  
Three Dimensional ◽  
Coronal Loops ◽  
Mhd Simulation ◽  
Mhd Simulations ◽  
Uniform Background ◽  
Energy Gains ◽  
Particle Behaviour

Aim. The aim of this work is to investigate and characterise non-thermal particle behaviour in a three-dimensional (3D) magnetohydrodynamical (MHD) model of unstable multi-threaded flaring coronal loops.Methods. We have used a numerical scheme which solves the relativistic guiding centre approximation to study the motion of electrons and protons. The scheme uses snapshots from high resolution numerical MHD simulations of coronal loops containing two threads, where a single thread becomes unstable and (in one case) destabilises and merges with an additional thread.Results. The particle responses to the reconnection and fragmentation in MHD simulations of two loop threads are examined in detail. We illustrate the role played by uniform background resistivity and distinguish this from the role of anomalous resistivity using orbits in an MHD simulation where only one thread becomes unstable without destabilising further loop threads. We examine the (scalable) orbit energy gains and final positions recovered at different stages of a second MHD simulation wherein a secondary loop thread is destabilised by (and merges with) the first thread. We compare these results with other theoretical particle acceleration models in the context of observed energetic particle populations during solar flares.

scholarly journals The role of streamers in the deflection of coronal mass ejections

2011 ◽  
Vol 7 (S286) ◽  
pp. 134-138
Author(s):  
F. P. Zuccarello ◽  
A. Bemporad ◽  
C. Jacobs ◽  
M. Mierla ◽  
S. Poedts ◽  
...  
Keyword(s):  
Current Sheet ◽  
Three Dimensional ◽  
Heliospheric Current Sheet ◽  
Field Of View ◽  
Physical Explanation ◽  
Filament Eruption ◽  
Mhd Simulations ◽  
Radial Evolution ◽  
Mass Ejection

AbstractOn 2009 September 21, a filament eruption and the associated Coronal Mass Ejection (CME) was observed by the STEREO spacecraft. The CME originated from the southern hemisphere and showed a deflection of about 15° towards the heliospheric current sheet (HCS) during its propagation in the COR1 field-of-view (FOV). The aim of this paper is to provide a physical explanation for the strong deflection of the CME. We first use the STEREO observations in order to reconstruct the three dimensional (3D) trajectory of the CME. Starting from a magnetic configuration that closely resembles the potential field extrapolation for that date, we performed numerical magneto-hydrodynamics (MHD) simulations. By applying localized shearing motions, a CME is initiated in the simulation, showing a similar non-radial evolution, structure, and velocity as the observed event. The CME gets deflected towards the current sheet of the larger northern helmet streamer, due to an imbalance in the magnetic pressure and tension forces and finally it gets into the streamer and propagates along the heliospheric current sheet.

scholarly journals Measurement of the Local Current Density Inside a Current Sheet Using a Rogowski Coil Array on UTST Merging Plasmas

2018 ◽  
Vol 13 (0) ◽  
pp. 1202093-1202093 ◽  
Author(s):  
Hibiki YAMAZAKI ◽  
Hirokazu FURUI ◽  
Kotaro YAMASAKI ◽  
Tomohiko USHIKI ◽  
Akira EJIRI ◽  
...  
Keyword(s):  
Current Sheet ◽  
Current Density ◽  
Rogowski Coil ◽  
Coil Array ◽  
Local Current Density ◽  
Local Current ◽  
A Current

scholarly journals Thermal and Hall-Current Instabilities in a Current Sheet and the Triggering of two Ribbon Flares

1993 ◽  
Vol 141 ◽  
pp. 119-122
Author(s):  
Li Sang Jae
Keyword(s):  
Magnetic Field ◽  
Thermal Stability ◽  
Current Sheet ◽  
Solar Flares ◽  
Hall Current ◽  
Growth Time ◽  
Filament Activation ◽  
The Magnetic Field ◽  
Thermal Stability Of ◽  
A Current

AbstractThermal stability of a current sheet is investigated when the magnetic field is not perfectly anti-parallel at the sheet. If the effect of Hall electric current is taken into account, a new instability (the Hall instability) appears. The result is applied to the activation of dark filaments often seen prior to solar flares. The growth time of the instability is evaluated and found to be consistent with the observed time scale of the filament activation.

Three-dimensional nonlinear mode coupling of the double-tearing instability

1997 ◽  
Vol 58 (2) ◽  
pp. 223-232 ◽  
Author(s):  
X. H. DENG ◽  
J. F. WANG ◽  
B. C. ZHANG ◽  
Z. G. CHEN
Keyword(s):  
Density Profile ◽  
Current Density ◽  
Solar Flares ◽  
Mode Coupling ◽  
Three Dimensional ◽  
Unstable Region ◽  
Tearing Instability ◽  
Start Up ◽  
Current Density Profile ◽  
Nonlinear Mode Coupling

The nonlinear development of the double-tearing instability and the mode coupling of different helicities are investigated numerically in cylindrical geometry. The results show that double-tearing instability arises with a central-hollow current-density profile, and the coupling of different low-poloidal mode numbers m leads to rapid destabilization of modes with higher poloidal mode numbers. This instability ultimately leads to the resistive reconnection of parts of the fluxes and reduces the current gradient in the unstable region. It seems likely that this process would accelerate current penetration in the tokamak start-up phase, and it also possibly plays an important role in the triggering of solar flares.

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